Meaning and Concept of
Control Charts
A control chart is a
graphical representation of the collected information. The information may
pertain to measured quality characteristics or judged quality characteristics
of samples. It detects the variation in processing and warns if there is any
departure from the specified tolerance limits.
The control limits on
the chart are so placed as to disclose the presence or absence of the
assignable causes of quality variation. This makes possible the diagnosis and
correction of many productions troubles and often brings substantial
improvements in product quality and reduction of spoilage and rework. Moreover,
by identifying certain of the quality variations as inevitable chance
variations, the control chart tell when to leave the process alone and thus
prevents unnecessarily frequent adjustments that tend to increase the
variability of the process rather than to detect it.
With the help of a
control chart it is possible to find out the natural capability of a production
process, which permits better decisions on engineering tolerances and better
comparisons between alternative designs and also between alternative production
methods. Through improvement of conventional acceptance procedures, it often
provides better quality assurance at lower inspection cost.
Structure and
Construction of Control Charts
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